Many different types of delivery systems for delivering beneficial agents such as pharmaceuticals for the prevention, treatment, and diagnosis of disease are known in the art. One type of delivery system is the osmotic delivery system in which an osmotic pressure gradient is created to draw an aqueous fluid into a beneficial agent containing member causing the beneficial agent to be delivered. Osmotic delivery systems generally include an implantable member forming a chamber containing the beneficial agent and an osmotic agent which draws an aqueous fluid through the walls of the implantable member causing swelling of the osmotic agent and delivery of the beneficial agent.
Some osmotic delivery systems include a single compartment implantable member and contain both the beneficial agent and the osmotic agent within this single compartment. These devices release the beneficial agent by allowing fluid to be imbibed through the wall of the implantable member into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall. The fluid imbibed into the device mixes with the beneficial agent to form an aqueous solution which is dispensed through an exit passageway of the device. Although these devices are effective for delivery of a beneficial agent which is stable and soluble in aqueous and biological fluids, the devices are ineffective for delivery of many types of beneficial agents which are not soluble or stable in aqueous fluids. Examples of osmotic delivery systems of this type include those described in U.S. Pat. Nos. 3,845,770 and 3,916,899.
Improvements in osmotic delivery systems are described in U.S. Pat. Nos. 4,111,202; 4,111,203; and 4,203,439. In these patents the delivery kinetics of the devices has been improved by allowing delivery of beneficial agents without the requirement for the beneficial agent to be soluble in an aqueous type fluid. These improved implantable osmotic devices include a first beneficial agent compartment separated by a film or piston from a second osmotic compartment. In these devices, the beneficial agent is delivered by imbibing fluid through the wall of the device into the osmotic compartment. As the osmotic compartment fills with fluid, the osmotic agent within the compartment swells and acts as a driving force causing the film or piston to move against the beneficial agent and deliver the beneficial agent through a delivery passageway.
The various osmotic delivery systems are designed to deliver a beneficial agent at a controlled rate which will vary depending on many factors including the osmotic material used, the permeability of the walls, and the physical configuration of the delivery device. Although osmotic delivery devices generally operate very reliably to dispense the desired amount of beneficial agent at the desired rate, it would be beneficial to be able to monitor the delivery of beneficial agent. For example, it would be desirable to be able to detect when the beneficial agent within the delivery device has been completely dispensed and a new device may be needed. It would also be beneficial to detect a malfunction of the device, for example, in some types of osmotic delivery devices employing a piston which separates the osmotic agent and the beneficial agent the piston may become frozen causing the device to malfunction. In a addition, monitoring of the delivery rate of the beneficial agent would be desirable to more accurately monitor and control treatment.
Some methods which have been contemplated for monitoring drug delivery from osmotic delivery systems include the measurement of residual amounts of delivered drug in the patient, or radiolabeling the drug composition for detection by X-ray. However, these monitoring methods involve a time delay.
Drug delivery rate s are generally determined f or a particular implantable osmotic device by testing the unimplanted drug delivery device and collecting and measuring the delivered drug in a collection vessel. However, these tests will not account for varying conditions which the drug delivery device will encounter when it is actually implanted within the patient. Therefore, monitoring of the operation of the implanted osmotic drug delivery device would be desirable.